Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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Page 1 of 4

1. The capillary tube, as an expansion device, is used in

All of these

Water coolers

Domestic refrigerators

Room air conditioners

2. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Carbon dioxide

Freon

Brine

Ammonia

3. A bootstrap air cooling system has

Two heat exchangers

Three heat exchangers

One heat exchanger

Four heat exchangers

4. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Normal cooling

None of these

Sub-cooling or under-cooling

Super-cooling

5. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

6. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

7. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Good electrical conductor

Large latent heat

Low boiling point

8. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Negative

Positive

Zero

9. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

5.12

2.15

10. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

Superheat the vapour

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11. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

Less

More for small capacity and less for high capacity

12. Most thermostatic expansion valves are set for a superheat of

15°C

20°C

10°C

5°C

13. Rating of a domestic refrigerator is of the order of

10 tons

0.1 ton

40 tons

5 tons

14. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

1.33

4.33

3.33

2.33

15. For obtaining high COP, the pressure range of compressor should be

Optimum

High

Any value

Low

16. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Compressor and condenser

Receiver and evaporator

Evaporator and compressor

17. The curved lines on a psychrometric chart indicates

Dew point temperature

Dry bulb temperature

Wet bulb temperature

Relative humidity

18. The value of C.O.P in vapour compression cycle is usually

Any one of the above

Equal to unity

Always less than unity

Always more than unity

19. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

20. A thermostatic expansion valve in a refrigeration system

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

Page 3 of 4

21. The operating pressure for refrigerating units using R-12 as a refrigerant is

2 bar

15 bar

30 bar

8 bar

22. The boiling point of ammonia is

-77.7°C

-33.3°C

-10.5°C

-30°C

23. Which of the following cycles uses air as the refrigerant?

Stirling

Bell Coleman

Carnot

Ericson

24. Critical temperature is the temperature above which

A gas will never liquefy

A gas will immediately liquefy

Water will evaporate

Water will never evaporate

25. The freezing point of sulphur dioxide is

-135.8°C

-77.7°C

-75.2°C

-56.6°C

26. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

Much below critical temperature

Near critical temperature of refrigerant

At critical Temperature

27. In a lithium bromide absorption refrigeration system

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

28. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant pressure

Takes place at constant temperature

Takes place at constant entropy

29. Cooling water is required for following equipment in ammonia absorption plant

Evaporator

Absorber

Condenser

Condenser, absorber and separator (rectifier)

30. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Equally

Less

Page 4 of 4

31. Freon group of refrigerants are

Toxic

Non-inflammable and toxic

Inflammable

Nontoxic and non-inflammable

32. The bank of tubes at the back of domestic refrigerator is

Evaporator tubes

Capillary tubes

Condenser tubes

Refrigerant cooling tubes

33. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

1: 3

1: 1

9: 1

34. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.67

0.376

0.6

35. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Dry bulb temperature of air

Ambient air temperature

Wet bulb temperature of air

36. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Saturated liquid

Superheated vapour

Wet vapour

37. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

38. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Carnot

Reversed Rankine

Rankine

39. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₂/ (T₂ - T₁)

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

40. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Piston type reciprocating

Centrifugal

Axial

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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